An isoflavone derivative is a representative flavonoid having excellent pharmacological efficacy, and a lot of capital is investigated in the development of functional plants having high content of the isoflavone derivative. Since isoflavone has a chemically similar structure as nonsteroid estrogen and has a similar physiological property as estrogen, isoflavone is referred to as phytoestrogen. Isoflavone has a similar structure as estrogen, i.e. female hormone, thereby showing useful bioactivity expected from estrogen. In particular, it has been reported that isoflavone reduces both the risk of osteoporosis after menopause, and plasma cholesterol. It has been also reported that isoflavone has an effect of reducing a risk of coronary heart diseases and has an excellent antioxidative activity.
Isoflavone is present in a glycoside form in which beta-glycoside is linked, or a non-glycoside from in which a sugar is removed. Examples of non-glycosides include genistein, daidzein and glycitein, and examples of glycosides include genistin, daidzin and glycitin. While unfermented foods derived from soybeans mostly include glycoside, fermented foods mostly include non-glycoside, because sugars are degraded from glycoside by the bacteria associated with fermentation.
Most isoflavone used as a food and medicinal material is extracted from soybeans and red clovers and used. Various breeding studies have been conducted to develop soybeans having high isoflavone content, but soybeans having isoflavone content of 4000 μg/g has been reported as the soybean having the highest level (see J. Agric. Food Chem. 2012, 60, 6045-6055). In addition, Korean Patent Publication 2003-93025 discloses a method of preparing germinating soybeans containing high concentration isoflavone by immersing washed soybeans in purified water, and then germinating them to increase isoflavone content by 40-70%. However, there is a drawback in that the isoflavone content is still low.
It has been reported that soybean leaves contain an extremely low amount of isoflavone derivatives. Specifically, soybean leaves contain daidzin (undetected), genistin (90 μg/g), malonyldaidzin (undetected), malonylgenistin (310 μg/g), aidzein (undetected), and genistein (undetected) (see BIOMEDICINE & PHARMACOTHERATY, 2002, 56, 289-295).